diff --git a/backend/internal/service/openai_responses_item_id.go b/backend/internal/service/openai_responses_item_id.go
index cb1522e4fb..5fc8bb77d5 100644
--- a/backend/internal/service/openai_responses_item_id.go
+++ b/backend/internal/service/openai_responses_item_id.go
@@ -50,7 +50,7 @@ func shouldStripOpenAIResponsesInputItemID(itemType, id string) bool {
 	if !constrained {
 		return false
 	}
-	return id == "" || !strings.HasPrefix(id, prefix)
+	return id == "" || len(id) > 64 || !strings.HasPrefix(id, prefix)
 }
 
 func shouldStripOpenAIResponsesNonPairCallID(itemType string) bool {
diff --git a/backend/internal/service/openai_responses_item_id_test.go b/backend/internal/service/openai_responses_item_id_test.go
index b300b22a2e..10fd5dd6e0 100644
--- a/backend/internal/service/openai_responses_item_id_test.go
+++ b/backend/internal/service/openai_responses_item_id_test.go
@@ -2,6 +2,7 @@ package service
 
 import (
 	"strconv"
+	"strings"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -29,6 +30,9 @@ func TestOpenAIResponsesInputItemIDPrefixUsesObservedOutputContracts(t *testing.
 		{itemType: "tool_search_call", id: "fc_123", strip: true},
 		{itemType: "web_search_call", id: "ws_123", strip: false},
 		{itemType: "web_search_call", id: "item_123", strip: true},
+		{itemType: "web_search_call", id: "ws_" + strings.Repeat("x", 60), strip: false},
+		{itemType: "web_search_call", id: "ws_" + strings.Repeat("x", 61), strip: false},
+		{itemType: "web_search_call", id: "ws_" + strings.Repeat("x", 62), strip: true},
 		{itemType: "custom_tool_call_output", id: "fc_123", strip: false},
 		{itemType: "custom_tool_call_output", id: "ctco_123", strip: true},
 		// Do not impose an inferred contract on output types for which there is
@@ -132,6 +136,19 @@ func TestSanitizeOpenAIResponsesInputItemIDsStripsEmptyKnownIDsOnly(t *testing.T
 	require.True(t, gjson.GetBytes(sanitized, "input.1.id").Exists())
 }
 
+func TestSanitizeOpenAIResponsesInputItemIDsStripsOversizedWebSearchID(t *testing.T) {
+	validID := "ws_" + strings.Repeat("x", 61)
+	oversizedID := "ws_" + strings.Repeat("x", 62)
+	body := []byte(`{"input":[{"type":"web_search_call","id":"` + validID + `"},{"type":"web_search_call","id":"` + oversizedID + `"}]}`)
+
+	sanitized, changed, err := sanitizeOpenAIResponsesInputItemIDs(body)
+
+	require.NoError(t, err)
+	require.True(t, changed)
+	require.Equal(t, validID, gjson.GetBytes(sanitized, "input.0.id").String())
+	require.False(t, gjson.GetBytes(sanitized, "input.1.id").Exists())
+}
+
 func TestSanitizeOpenAIResponsesInputItemIDsStripsOnlyNonPairCallIDs(t *testing.T) {
 	body := []byte(`{"input":[
 		{"type":"message","call_id":"remove_message","content":"hi"},